The incorporation of antidandruff agents into anionic surfactant-based hair shampoos is well known. The individual antidandruff agents must not only relieve the flaking and itching symptoms of dandruff, but also be substantive to the skin and hair in order to extend the antidandruff agent's efficacy from one treatment to the next. These properties are most often found in compounds not soluble in aqueous media, and this inherent insolubility of the antidandruff agents makes formulation of a stable, aqueous, anionic surfactant-based antidandruff shampoo a difficult problem.
In order to incorporate such effective, sparsely soluble antidandruff agents as zinc pyrithione or sulfur into aqueous anionic surfacant-based hair shampoos, one or more suspending agents are required to keep the antidandruff agent homogeneously dispersed throughout the aqueous solution. Failure to adequately suspend the antidandruff agent leads to eventual shampoo separation as the antidandruff agent settles to the bottom of the container, and results in poor dandruff control and consumer complaints. Early antidandruff shampoo compositions used bentonite clay as the suspending agent, however, the trend has been to avoid bentonite since it gives the shampoo a dirty appearance and dries the hair due to the substantial oil absorption characteristic of bentonite. As a result, there has been a continuous search for suitable suspending agents capable of effectively dispersing antidandruff agents such as zinc pyrithione or sulfur.
In general, compositions containing insoluble particulate matter require a suspending agent to assist in dispersing the particulate matter evenly throughout the composition. Depending upon the ultimate use of the composition, the suspending agent may be any one of a number of inorganic minerals or synthetic or natural polymers or gums. Among the most often used suspension agents are colloidal aluminum oxide, modified magnesium aluminum silicate, xanthan gum, fumed silica, algin products, polyacrylic acid, sodium carboxymethylcellulose, hydroxypropylcellulose, synthetic sodium magnesium silicate, colloidal attapulgite clay, lignins and alkanolamides. In most compositions, the addition of a suspending agent at a great enough percentage to adequately suspend the particles in solution leads to an increase in viscosity.
Common hair shampoos are known to contain an effective low-to-non-irritating amount of an anionic surfactant, usually an alkyl sulfate, as a principal cleansing agent. Hair shampoos also include other components to improve product efficacy, stability and consumer acceptance. Therefore, any antidandruff agent and additional suspending agents added to a basic hair shampoo is expected to add antidandruff properties to the shampoo without detracting from the cleaning efficiency and aesthetic appeal of the shampoo. Unfortunately, the antidandruff agents and necessary suspending agents often adversely affect the foaming characteristics of the shampoo composition. Consumers perceive a substantial benefit in copious suds formation, since they incorrectly equate copious foam with excellent cleaning, and poor sudsing with inferior shampoos. The decreasing foaming capability of the antidandruff shampoos may be overcome by increasing the surfactant level of the shampoo, however, this option usually is avoided due to economic factors and oil extraction from the hair by detergent overformation.
Consumer acceptance of antidandruff hair shampoos also is influenced by the viscosity of the shampoo. The ideal shampoo should be thick enough to appear concentrated and not too run out of the container or hand to easily during application, and be thin enough for easy dispensing from the container, ease of application to the hair and even distribution over the scalp. These characteristics usually are found in a viscosity range from about 2000 cps to about 8000 cps. Some antidandruff suspending agent compositions tend to increase the viscosity of the shampoo outside consumer acceptable limits.
The Winkler U.S. Pat. No. 4,470,982, discloses a suspending agent composition for antidandruff agents including about 4% to about 6% of either the ethylene glycol esters of fatty acids having from about 16 to about 22 carbon atoms; alkanolamides of fatty acids having from about 16 to about 22 carbon atoms; or alkyl (C.sub.16 --C.sub.22) dimethyl amine oxides to produce antidandruff shampoo compositions of good viscosity and acceptably low separation. In accordance with the Winkler patent, the levels of suspending agent, surfactant and alkanolamide are critical to the utility of the shampoo compositions.
In accordance with the present invention, anionic surfactant-based antidandruff shampoo compositions show substantial and unexpected reduction in shampoo separation, while maintaining acceptable shampoo viscosities and foaming levels, by including a suspending agent composition comprising a suspending alkanolamide and/or a wax ester in conjunction with an ethylene-maleic anhydride resin or polyacrylic acid resin. The suspending agent composition is incorporated into the antidandruff shampoo composition at a low levels of about 1% to about 3% by weight of the shampoo composition, thereby minimizing or avoiding any deterioration of foaming characteristics or viscosity of the shampoo.